The wind rotor is understood as the assembly of components of the wind turbine rotating outside the nacelle. These components are the blades, hub and blade pitch control mechanism. From a design and manufacturing standpoint, each component is considered to be an independent element that must subsequently be assembled. In large wind turbines, the most complex joint to establish is between the blade root and hub, whose joint is in turn aligned with the fixed/mobile track unit and bearings that make up the blade pitch control mechanism.
Large size wind turbine blades are hoisted up and assembled on the wind turbine using hoisting methods that normally require two cranes. One of the cranes of superior height than the hub's height and the other one of smaller size to properly guide hoisting from the area at the tip of the blade.
The main difficulty of these hoisting methods lies in the unions between the lifting slings, or hoisting cables, and the hoisting points on the blade root. These hoisting points must withstand a significant load corresponding to the largest part of the weight of the blade. Further, the inserts in the blade root cannot be used for securing the slings, since, in the last stage of blade-to-hub assembly, the hub-fastening long bolts must be previously fit into the inserts. On the other hand, given that the blades are made of pieces of low thickness composite material, designing a mechanical joint between the hoisting points and the laminate without damaging the structure of the blade by deforming the initial circular shape, is complicated.
The closest state of the art corresponds to different ways of fastening the hoisting slings with the union points directly applied to the blade root as can clearly be seen in the drawings of patents DE 1995516 and EP 1101936. The solutions shown by these patents are intended for small-sized blades, since as the size of the blade increases, numerous points in the process become even more complicated: the deformation endured by the blade structure under its own weight during hoisting causes the blade root to ovalize and lose the tolerances necessary to readily align all the blade root inserts with the blade bearing holes (those corresponding to the hub) without difficulty. The present invention is directed to avoid the use of two cranes, thus minimizing costs derived from renting, achieving a hoisting method that merely requires lifting points on the hub and anchor points on the ground. Similar to patent P200603165 held by the same applicant. Thus, the invention keeps the hub-fastening long bolts and in turn incorporates elements that prevent the circular section of the blade root from deforming.